Filimin is a lamp that turns colors when you touch it and uses a cloud service to synchronize colors with its “group” of lamps anywhere in the world that has WiFi. John Harrison invented it last Christmas as a way for his family to maintain emotional contact across the continent and beyond — touch the lamp and it lights up in a new color to let your family see that you’re thinking of them before it eventually fades to black again.

I’ve already backed the project but it’s only 30% of the way to its $50,000 goal with 15 days to go. If it sounds interesting to you, too, please check it out, back the project, and help ensure that I end up getting my set.

A common strategy in the world of hobby robotics is to modify a servo for continuous rotation to use to drive the wheels of a tabletop robot.

On its own, the servo takes power, ground, and a position input and moves the shaft within a range of rotation to match the angle requested on its input wire. It has one or more stops in its gearbox to prevent it from rotating past the end of its range; these need to be removed. It also has a potentiometer as part of its positioning system, which — for the usual modification — needs to be tricked into thinking it’s always centered. The modified servo then runs at full speed forward or backward trying to reach a requested position and thinking it has never succeeded in doing so; and the controller requires extra, external rotation sensing if you want to detect what the servo has actually done so far.

I wanted something a little different — PWM H-bridge control of the servo’s motor for variable speed forward and backward and access to the potentiometer to detect position (crudely and at low speed) and count wheel rotations (acceptably and at high speed). This is actually an easier modification — but, though I’m surely not the first to do it, I’ve not run across it before. I started last night.

I’ve been busy enough that I haven’t done much tinkering or blogging lately, but I’m preparing to use the power of peer pressure to change that.

I’ve been interested in FPGAs (field-programmable gate arrays — big chips full of digital logic and links that you program to turn them into the circuits you want) for a long time. I understand them conceptually but have never had the chance to work with them.

In November of 2008, I found and ordered the Terasic DE0-Nano FPGA trainer / development board featuring the Altera Cyclone IV 4C22 FPGA. It has onboard LEDs, pushbuttons, DIP switches, accelerometer, and A/D converter; USB host connectivity; a set of tutorials to get you started; and (at least at the time) free host development software for Windows and Linux (which I can’t find online right now). And it’s $86 at Digi-Key.

After some period of not doing anything with it, I mentioned it to John Harrison and he suggested that he get one (and did) and that we challenge each other to go through the tutorials and then expand our knowledge by creating further interesting projects. Which we hadn’t done yet when we reminded each other about it … in December of 2013. And — you guessed it — haven’t done it yet.

Another reminder last month, and John boldly said, November 1! (He cunningly left off the year.)

The smaller the battery, the more important it is not to forget that the desulfator / dewhiskerer is on. This was, as I recall, only about a fifteen-minute overdose. The magic smoke, I assure you, got out.

The left two are open — you can see the broken wire at the bottom of the left coil and the top of the middle coil. (As always, click for full-sized image.) The right one is shorted and I haven’t found where.

I find it interesting that these are wound with round wire and the replacements are wound with flat-cross-sectioned copper “ribbon,” to get more current capacity in the same vertical space.

I tend to assume that batteries I happen upon will not be charged. Also that lead-acid batteries I happen upon will be low on water, even so-called sealed lead-acid batteries.

I wanted to start charging the batteries from my “new” scooter while working on other aspects of the project and the scooter didn’t come with a charger — I’ll deal with that later. Not knowing much about the wiring circuit yet, I didn’t want to connect an external charger to the batteries while they were still in-circuit and chance damaging the speed controller, so I needed to disconnect and remove them.

In spite of being “sealed,” you can pry off the cover (preferably after cleaning, which I did first with Goo-Gone and then with dish soap and water)

and get to the cell caps, each with a little absorbent pad in case the cell venting carries too much moisture.

I could see no water in any cell of either battery. I borrowed a jug of distilled water from my folks (I don’t know why Mom always has some, but she does) and started filling them up … after taking measurements.

Battery 1

Battery 2

Initial

11.68 V

9.99 V

After adding water

11.62 V

9.92 V

I filled each cell, waited for air bubbles to trickle to the top, refilled, waited, refilled, waited … I’m guessing between the initial fill and while charging, I ended up putting at least 10 ml of water into each cell.

Then put battery 1 on my variable power supply with the voltage set to 13.8 V and the current limited initially to 0.1 A, raising the current limit to 0.3 A as it was clear that nothing horrible was happening. I checked on it every half-hour to hour, frequently refilling at least one cell in which I could no longer see any water.

After about four hours, it was up to 13.5 V. The water level in the cells had risen to overflow the opening and fill each reservoir. If I watched long enough, I could see the water in a couple of cells <pop>, indicating they were just starting to gas and it was time for me to stop this method of charging for the day. (More on that on a subsequent day, hopefully tomorrow.)

While battery 1 was charging, I was also checking water levels in battery 2 and refilling low cells, just sitting on the counter.

Recalling that it had an initial 10 V charge to battery 1′s 11.7 V, noting that they had been connected in series, and knowing that the worst cell in a battery generally has a cascading failure, I expected a different charging experience from battery 2, and I was quite right.

I connected it to the power supply and it immediately showed 13.8 V at a 0.1-A current draw. Now, about an hour later, it’s at 13.5 V and 0.3 A and most of the cells have overflowed. It’s nearly done charging but I haven’t put nearly as much energy into it as I was able to put into battery 1 — that is to say, it’s not “taking” as much of a charge.

Battery 1

Battery 2

Initial

11.68 V

9.99 V

After adding water

11.62 V

9.92 V

After charging

12.68 V

12.48 V

Tomorrow, schedule willing, a load test and an attempt at desulfation.

This afternoon I learned of the recently- (?) opened Deja Vu thrift store in Newton and made my first purchase: a Razor E100 scooter in considerable state of disassembly. I’ve long thought that electric scooters looked like fun …

All of the wires are cut, the deck is missing, the rear wheel was unattached, naturally the drive belt was missing, and no charger.

$10. I bought it. Sounds like a fun project, eh?

The battery and speed-control bucket could use some repair but seems at least functional. I started working on the batteries but as soon as my brother was available redirected my attention to reattaching the rear wheel.

The rear wheel is belt-driven and needs to be positioned to align with the motor pulley but the spacers were absent and it slid freely from side to side.

A trip to the hardware store resulted in a roll pin with ID slightly larger than the 1/4″ axle diameter and length slightly greater than the two spacers needed, for $1.89. Then my brother’s giant chop saw made short work of creating two pieces from one.

Touched up a bit on the bench grinder, ends rounded over with a file, and interiors cleaned out with a round file, spacers fit perfectly and the rear wheel bolts on securely. We “kicked” our way up and down the driveway and are eager to get the scooter powered up.

I have no CC notices posted for the whole site (though I’d be happy to); but of course the Berne Convention provides for automatic copyright upon creation and publication of a work, so this is a blatant copyright violation.

Regardless, why is an eBay seller with only 110 feedbacks (vs one who does business on a scale of 110,000) too lazy to take their own picture of what they claim to have for sale?

And Linux. And old, high-programming-voltage EPROMs. And USB, naturally. If you know of such a thing, give me a shout in the comments — I can’t find any on Google, and I find plenty of links to other people who also couldn’t find them.

6502 Microprocessor, Apple ][, and Asteroids

A couple of weeks ago, I went to an annual holiday lunch with former coworkers and got to visit with an old friend. He was reminiscing about 6502 assembly programming on the Apple ][ and wondered whether I'd know where he could get one. I told him that I could probably loan him one or two; but (with a mischievous glint in my eye) that I have a couple of upright Asteroids arcade games and they run on 6502s and I’ve always wanted to reprogram one and write my own game.

Bump, set, spike. Yeah, he’s interested.

It’s not a completely impractical idea. I have a large schematic set that includes the addressing of the memory-mapped I/O and some rudimentary information on the operation of the vector generator board. There’s even a project to comment the disassembled ROM, which would give further hints about how to interface to the hardware.

If one were to undertake such a project, one would really like to use a USB-attached EPROM emulator so one could dump new code into the machine frequently and rapidly for testing and development. But at a bare minimum, one would need a stack of EPROMs and a programmer and ideally a ZIF-socket daughterboard to fit into the original EPROM socket and make it easy to swap EPROMs. As I have no Windows machines and do my electronics development on a synchronized fleet of Mac and Linux machines, a commercial EPROM programmer that I can use is going to be a little bit hard to come by.

Yes, I could run Windows under virtualization on my Mac; I think I may even be able to get a legal copy through my campus’s license agreement. But I’m not interested in going that direction unless I have to.

Anyone know where to find new, large-capacity SCSI-2 fast/wide hard drives? A computer I supported at a hospital a long time ago has a failing hard drive and I’m happy to assist with replacement but I’m not coming up with any sources for the hardware.